At this rate, it will happen in the ending.
This is why Abby has the butt plug, so it can happen in the end.
Prediction: Next update, Frank will have another Fairy Abby dream where she bangs his brains out. Simultaneously Abby awakens to hear him talking in his sleep with a huge erection, so she decides to give him a hand job to help him out. He wakes up just as he's ejaculating and Abby gets her hands covered, which she then licks off.
This leads to a new Abby House Rule: Whenever Frank cums at home he has to give Abby a deep smoochy kiss (this covers wet dreams, tugging one off in the shower to keep her from seeing his boner, etc.) since she presumes those are all because of her sexy body and his repressed attraction. This leads to some confusion for Abby when she returns home from school after he's been working with Mei all day and is greeted by Frank with a 20 minute makeout session.
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